The present invention relates to a circuit tape, a semiconductor device, and a method of manufacturing the same, which are superior in electrical characteristics, mounting reliability, and assembling easiness, and are responsive to the requirements for high density mounting, multipins mounting, and fast transmittance.
Currently, in the continuing effort to improve electronic devices to provide high performance, the demand for high integration and high density mounting of semiconductor elements has become strong. Therefore, semiconductor elements have been improved to achieve high integration and high performance, such as in LSI, VLSI, and ULSI devices, and there has been increase in the capacity, the number of pins, the speed, and power consumption thereof. In responding to such advances, the package structure of the semiconductor device for multipins has been changed from a structure, in which connecting terminals are provided at two sides of the semiconductor element, to an advanced structure, in which the connecting terminals are provided at all four sides of the semiconductor element. Furthermore, in order to respond to increasing the number of pins, a grid array structure has come to be used in practice. The grid array structure is a structure of a semiconductor element, in which the connecting terminals are provided in a grid array over the entire mounting surface of the semiconductor element by using a multilayer carrier substrate. The grid array structure includes a ball grid array structure (BGA), which has a shortened connecting terminal length in order to make fast signal transmission possible. The ball type structure of the connecting terminal increases the width of its conductor; therefore, the ball structure is also effective in decreasing inductance. Currently, in order to respond to the requirement for fast signal transmission, organic materials having a relatively low dielectric constant have been investigated for use in the multilayer carrier substrate. However, the organic materials have generally a larger thermal expansion coefficient than the semiconductor element, and so thermal stress generated by the difference in thermal expansion becomes a problem from the point of view of connection reliability, and so on. Recently, a structure which does not use a carrier substrate has been proposed for the BGA package.
More particularly, a new semiconductor element package structure has been disclosed (U.S. Pat. No. 5,148,265), in which the connection reliability is improved by using an elastomer material having a low modulus of elasticity for reducing the thermal stress generated by the difference in thermal expansion between the semiconductor element and the mounting substrate. The proposed package structure uses a circuit tape composed of a polyimide and the like, instead of a carrier substrate, for electrically connecting the semiconductor element and the mounting substrate. Therefore, the electrical connections between the semiconductor element and the circuit tape are effected by a wire bonding method or a bonding connection with leads, and the circuit tape and the mounting substrate are electrically connected by soldering ball terminals. As the elastomer material of the prior art, a silicone material is generally used since this is a material having a low modulus of elasticity and a superior heat resistance. As a general method for forming a stress buffer layer with a silicone material, the steps of printing an uncured liquid resin on the circuit tape using masks, and subsequently, curing the printed resin, are generally used. However, the above method has problems, such as a difficulty in maintaining the flatness of the buffer layer obtained by the printing, and the complexity of the printing process, which requires a long time for the printing, is disadvantageous. Accordingly, the above method is not suitable for a mass-production process, and so the problems which undesirably affect the assembling yield and reliability of mounting caused by the difficulty in maintaining the flatness of the buffer layer are yet to be solved.